In order to solve the problem of interference between structural dynamic components and vehicle multi axial effects in the measured time history response of bridges, a damage diagnosis method for simply supported beam bridges based on the identification results of deflection influence line was proposed. Firstly, the time history response of the bridge was preprocessed by variational mode decomposition and wavelet transform to realize the stripping of the dynamic components of the measured response of the bridge. Secondly, the multi axle vehicle information matrix and the influence line identification model were established, so as to eliminate the multi axle effect of vehicles in the measured response of the bridge. Thirdly, the quasi static deflection influence line of the bridge was identified by Tikhonov regularization method. Finally, the influence line difference curvature index was used to locate the bridge damage. The feasibility and effectiveness of the proposed method were verified through a vehicle bridge coupling model under moving loads of two and three axle vehicles. The research shows that the two proposed identification methods of influence line are effective and reliable, and the identification effect of influence line is less affected by vehicle speed and vehicle type, among which the variational mode decomposition method is more effective in identifying bridge influence line for damage diagnosis under high-speed driving.